1. Field of the Invention
The present invention relates to porous ceramics provided with amorphous pore surfaces useful for treating various kinds of drain water and waste liquid which treatment now becomes a serious problem, such as river or lake water and industrial drain water containing hard to remove phosphorus and nitrogen, waste water containing organochlorine compounds such as tetrachloroethylene, piggery excreta waste water containing organic nitrogen at high levels, waste water containing heavy metals such as lead, hexavalent chromium, nickel, mercury, zinc, cadmium, selenium, etc., drain water from dairy factories, aquatic food processing factories and slaughter houses which contains water soluble protein at high level, drain water from pulp industry, photographic developer waste water, car wash drain water containing a mixture of polishing wax and detergent and the like, and a method for preparing the same and a method for treating various kinds of drain and waste water by the use of the porous ceramic and activated carbon.
2. Description of the Related Art
Recently, one serious social problem is pollution of water areas, for example, lake eutrification caused by an excessive supply of nutritive salt such as phosphorus, nitrogen, etc. from river basins thereof, and further, an inflow of similar nutritive salt into basins, etc. due to concentration of both population and industry, which results in abnormal breeding of algae and an occurrence of red tide thereby damaging fisheries.
As a lake is closed water basin where water remains therein long enough to easily precipitate contaminants, water pollution thereof is more serious than that of rivers and sea areas and causes difficulty in filtering tap water, problems of off-flavor or -taste and troubles of a water use in the field of fisheries, etc.
Conventional methods for treating drain water and waste liquid containing phosphorus and nitrogen are generally known as in the following. As to phosphorus, the most general is a coagulation method using a coagulant, which comprises, for example, an anaerobic-aerobic primary treatment, a coagulating secondary treatment using a coagulant and a reverse osmotic and ion exchanging final treatment. Although an absorbing or crystallizing treatment is also known, the coagulation method is often used for industrial drain water, while the anaerobic-aerobic method is used for sewage, in general. As to nitrogen, various kinds of treating method are known such as nitrification-denitrification, ammonia stripping, selective ion exchange, break-point chlorination, catalytic oxidation and the like, although the anaerobic-aerobic treatment (nitrification-denitrification) and a combined method of the coagulation and anaerobic-aerobic treatment are practically used among others.
Tetracloroethylene is an odorous liquid organochlorine compound having higher specific gravity and used as a solvent for laundry, metal cleaning, etc., but as is well known, exhibits effects in humans and causes headache, giddiness, hepatic dysfunction and the like. Trichloroethylene is also an odorous liquid organochlorine compound having higher specific gravity and mainly used as a metal cleaning solvent because of adequate compatibility thereof with oil, but as is well known, causes headache, giddiness, hepatic dysfunction and the like.
In a conventional method for generally treating waste liquid and drain water containing organochlorine compounds such as tetrachloroethylene, trichloroethylene, these toxic substances were recovered by means of an activated carbon unit or a moisture separating unit as a pretreatment to reduce concentration thereof in the waste liquid and drain water, followed by an aeration treatment.
Heretofore, it has been known to treat various kinds of waste water by the use of porous ceramics.
JP-A No. 58-205,516, for example, describes a superior tubular cartridge-type ceramic filter for selectively removing chemicals, heavy metals, etc. in which a silicastone-clay mixture is added with feldspar and alumina powder, kneaded with saw dust and water to form a muddy molded article and calcined at a temperature of 1,100 to 1,200.degree. C.
JP-B No. 1-60,317 describes a waste water treating system for sewage, etc. which comprises a filter layer consisting of sand and gravel layers formed on the bottom of a treating tank, a treating layer formed by laminating porous ceramic particles on the filter layer and air diffuser tubes arranged between an upper surface of the treating layer and a bottom surface of the filter layer.
JP-A No. 61-136,490 describes an aeration-type waste water treating system in which filter materials comprising porous ceramic particles filled in a perforated material such as a net are vertically arranged at certain spaces on a location so as to cross the direction of a waste water flow in an aeration tank.
JP-B No. 1-42,758 describes an advanced aeration-type waste water treating system which comprises an aeration tank in which filter materials comprising porous ceramic particles filled in a perforated material such as a net are vertically arranged at certain spaces on a location so as to cross the direction of a waste water flow in the aeration tank, a filter layer connected with the aeration tank through a tube body and consisting of sand and gravel layers on an bottom portion thereof, a treating layer formed by laminating porous ceramic particle on the filter layer and diffuser tubes arranged between an upper surface of the treating layer and a bottom surface of the filter layer.
JP-B No. 2-1,558 describes a method for biologically treating waste water such as domestic, general industrial or food processing waste water in the main in a treating medium containing porous ceramics and wood chips as main components.
JP-B No. 63-66,247 describes a method for treating emulsifiable oil containing waste water in which a mixture of porous ceramics and activated carbon is filled as a filter material in a cylindrical body to use as a filter system.
JP-A No. 60-261,586 describes a method for removing metals, metal ions and organochlorine compounds in drinking water such as tap water by means of a filter system with an intermediate layer of activated carbon between porous ceramics layers.
Further, as a method for preparing porous ceramics useful for the treating the above mentioned drain and waste water, JP-A No. 61-291,473 describes a method for preparing porous ceramics by compounding a pore forming material to a slurry of clay mineral material added by and mixed with water followed by drying and calcination, characterized in that the pore forming material is subjected to a pretreatment to combine a metal powder or organometallic compound to a pore surface, while the calcination is conducted in an atmosphere of air or nitrogen.